Metal garage doors are sturdy and do not require a lot of maintenance. They do need a good coat of paint to protect the metal from the elements. Exposed bare metal can rust. Rust weakens the structure of the metal. When paint chips, scratches or wears off a metal garage door, it is time for a new paint job. Another good time to paint the garage door is when the exterior of the house has been painted a new color. The garage door color should look nice next to the exterior house color. With a good paint job, a metal garage door looks attractive and will last a long time.
Spray off the metal garage door, using a hose with a spray attachment nozzle, to clean away dirt and debris.
Scrub the garage door vigorously using a strong detergent and an abrasive scouring sponge. Use circular motions when scrubbing the door. The detergent and scrubbing action removes dirt and rust and roughens the surface so that it will hold paint better. Any strong detergent is sufficient. You can purchase a strong detergent at a hardware store. Undiluted Simple Green works well. Kitchen scouring pads work well.
Rinse the detergent off the garage door using a hose with a spray attachment nozzle. Allow the door to air dry.
A primer base coat makes the final color coat stick better to the garage door. Open a can of acrylic paint that is made for outdoor use. Stir the paint using a long stick to mix thoroughly. Pour the paint into the spray gun. Acrylic paint is a good choice for garage doors, because the paint is flexible and will bend instead of chip off during garage door movement. This is important because garage doors move often during normal use, when they are opened and closed.
Apply a base coat to the garage door using a spray gun. Spray a thin coat of paint on the garage door using long strokes. Allow the base coat to dry for 2 to 24 hours, depending on the brand of paint. Look at the paint manufacturer documentation to find the suggested drying time.
Prepare the color coat. Rinse out the spray gun canister to remove the primer. Dry the canister. Open the acrylic color paint. Thoroughly stir the paint with a long stick and pour the paint into the spray gun.
Paint the color coat on the garage door using the spray gun. Only apply a thin coat of paint. The paint should be fully dry in 24 hours. If desired, paint a second coat of paint on the garage door.